replace potmeter on motorctrl with digital potmeter to use arduino to controll

Other Hardware General Electronics
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  1. The AC fans are likely synchronous or induction motors so can't be speed controlled by a triac circuit.
    Consult the datasheet for the fans concerned...

  2. That circuit is high voltage, so cannot possibly use a digipot on it, the voltages across the pot will be in
    the 100's of volts range. Its also floating on top of live mains voltage so needs full galvanic isolation anyway.

  3. You can control temperature by turning the fans on and off on a timescale of minutes, use PID and very
    low frequency PWM. This is commonly done for heating controllers, and this problem is similar except
    you are switching on the cooling. Suitable SSRs or relays with snubber circuits could be used (ac fans are
    inductive enough to require good snubbing).